JP5376604B2 - Lead-free brass alloy powder, lead-free brass alloy extruded material, and manufacturing method thereof - Google Patents

Abstract

Brass alloy powder has a brass composition formed by a mixed phase of ±-phase and ²-phase, and contains 0.5 to 5.0 mass% of chromium. The chromium includes a component that is solid-solved in a mother phase of brass, and a component that is precipitated at crystal grain boundaries.

Description

  The present invention relates to a high-strength brass alloy, and particularly to a brass alloy powder and a brass alloy extruded material that do not contain lead harmful to the environment and the human body.

  In recent years, environmental problems have been greatly highlighted, and attention to this point is also necessary in alloy development. 6/4 brass has moderate strength, good mechanical properties, and is non-magnetic, so it is not only used as a machine part, but also used in a wide range of gas pipes, water pipes, valves, etc. Has been.

  In order to improve the workability of a member made of 6/4 brass, several percent of lead is usually included in the alloy composition. When this lead-containing brass member is used for a water pipe, lead may be dissolved into the water supply.

  In order to solve the above problems, lead-free brass materials are being developed. As a conventional development example, tin is added as disclosed in Japanese Patent Application Laid-Open No. 2000-309835 (Patent Document 1) and International Publication WO98 / 10106 (Patent Document 2), in which bismuth is added instead of lead. In this case, a γ phase is precipitated, and silicon fine particles are dispersed. Some of these developed technologies not only realize lead-free, but also simultaneously improve the strength of brass itself to expand the application range.

  However, at present, the addition of bismuth has only obtained the same strength as the addition of lead. Both bismuth and lead are elements that lower the strength of brass when added, and do not contribute to improving the strength of the brass member. As disclosed in Japanese Patent Application Laid-Open No. 2000-309835 (Patent Document 1) and International Publication WO98 / 10106 (Patent Document 2), the method of precipitating the γ phase by the addition of tin, Although the strength and the like are improved, the deformability of the brass member is greatly reduced and the workability is inferior. In addition, the problem of brittle fracture starting from the γ phase also arises. The method of dispersing the silicon fine particles contributes to the improvement of the mechanical strength of the brass alloy member, but has a disadvantage that the machinability of the member becomes inferior.

  46th Annual Meeting of Copper and Copper Alloy Technology Conference (2006), pp. 153-154, Katsuyoshi Kondo et al. (Non-Patent Document 1) entitled “Characteristics of completely lead-free free-cutting brass alloy by powder process” and graphite particle-dispersed free-cutting properties based on powder metallurgy. A method for producing a brass alloy is disclosed. The merit of adding graphite is that it can be made completely lead-free and that the graphite floats on the molten brass at the time of recycling, so that the separation is easy. On the other hand, the strength improvement of the brass member by the added graphite cannot be expected. Therefore, when adding graphite, the strength improvement technology of the brass member using the powder metallurgy method should be considered.

  In general, when a low melting point metal is melted in a high melting point metal at a high temperature, the low melting point metal vaporizes rapidly during melting due to the high vapor pressure of the low melting point metal, resulting in a desired alloy composition. Is difficult to control.

  Brass is an alloy of copper and zinc. If a high melting point metal is added to this brass, the strength may be improved. However, the boiling point of zinc is as low as 907 ° C., and it is not easy to add chromium having a melting point of 1907 ° C. or vanadium having a melting point of 1902 ° C. Increasing the temperature of the brass in the liquid phase inevitably increases the amount of zinc evaporated, and the alloy composition suddenly changes in the direction of copper richness.

  Examples of the melting method of the refractory metal include an electron beam melting method and a hydrogen plasma arc melting method, but these methods are not suitable for mass production but are used for batch processing of rare metals. Moreover, these methods cannot prevent evaporation of the low melting point metal.

  Although a method of adding a molten high melting point metal to a low melting point metal is also conceivable, heating and melting the high melting point metal to its melting point is not industrially appropriate and difficult to mass-produce. It is. Therefore, generally, a method using the thermite reaction of an oxide or a method of adding a mother alloy having a lower melting point is performed.

Japanese Patent Laid-Open No. 10-168533 (Patent Document 3) discloses a method of adding an alloy component to zinc. This publication describes that a mother alloy was used for the addition of chromium, but it can be seen from the thermal equilibrium diagram of Zn—Cr that chromium hardly dissolves in zinc. In other words, it can be understood that Zn ₁₇ Cr or Zn ₁₃ Cr as a compound is dispersed in a zinc matrix. When this mother alloy is added to zinc, only the component ratio of zinc increases, and the chromium compound does not change. As described above, it is very difficult to dissolve a high melting point metal which is a non-solid solution element in a low melting point metal, and it is necessary to develop another method.

  The addition of chromium into copper is more advanced than zinc-containing alloys. As representative ones, there are techniques disclosed in Japanese Patent Application Laid-Open No. 11-209835 (Patent Document 4) and Japanese Patent Application Laid-Open No. 2006-124835 (Patent Document 5). In the methods disclosed in these publications, chromium, zirconium, tellurium, sulfur, iron, silicon, titanium or phosphorus is contained in copper. Both are precipitation-type copper alloys that precipitate copper and zirconium compounds as a strengthening phase, but unlike zinc-containing alloys, they can be alloyed even at high temperatures, making these materials easy to produce. I have to.

  In the development process of leadless brass, it is known that it is effective to apply the powder metallurgy method as a method of adding graphite. This is largely because the mixing of graphite and brass has become possible by using powder. Even if the addition of graphite is attempted by an ordinary melting method, the graphite floats on the brass melt due to the difference in specific gravity between them, and cannot be dispersed in the brass.

JP 2000-309835 A International Publication No. WO98 / 10106 JP 10-168533 A JP-A-11-209835 JP 2006-124835 A

46th Annual Meeting of Copper and Copper Alloy Technology Conference (2006), pp. 153-154, Katsuyoshi Kondo and others

  The inventors of the present invention have been working on the development of brass to which graphite is added as part of the development of a lead-less brass alloy. However, the graphite particle-dispersed lead-free free-cutting brass alloy has the same strength as the lead-containing free-cutting brass alloy, and the strength is not dramatically improved.

  An object of the present invention is to provide a brass alloy powder that contributes to improving the strength of a brass alloy member.

  Another object of the present invention is to provide a brass alloy extruded material having excellent mechanical strength.

  Still another object of the present invention is to provide a brass alloy member having excellent mechanical strength.

  Still another object of the present invention is to provide a method for producing a brass alloy extruded material having excellent mechanical strength.

  The brass alloy powder according to the present invention has a brass composition composed of a mixed phase of an α phase and a β phase, and contains 0.5 to 5.0% by mass of chromium. The chromium contains a component that dissolves in the parent phase of brass and a component that precipitates at the crystal grain boundary.

  If the aggregate of the brass alloy powder is extruded, a brass alloy extruded material having excellent mechanical strength can be obtained. In order to obtain a desired mechanical strength, the chromium content needs to be 0.5 mass% or more. In order to increase the mechanical strength of the brass alloy extruded material finally obtained, the chromium content in the brass alloy powder may be increased. However, 5.0 mass% is the limit from the viewpoint of production at the present time. is there. A more preferable chromium content is 1.0 to 2.4% by mass.

  The chromium component that is forcibly dissolved in the mother phase of brass contributes to the improvement of the yield strength by suppressing the dislocation movement in the crystal. On the other hand, the chromium component precipitated at the crystal grain boundary suppresses the grain boundary sliding, causes extreme work hardening, and contributes to the improvement of the tensile strength. The components that dissolve in the mother phase of brass include a component that dissolves and disperses in the mother phase, and a component that disperses as a precipitate in the mother phase.

  The brass alloy powder may contain at least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum, and tin.

  Preferably, the brass alloy powder is a rapidly solidified powder, and more preferably a powder that has been rapidly solidified by a water atomization method.

  A brass alloy extruded material according to the present invention has a brass composition composed of a mixed phase of an α phase and a β phase, contains 0.5 to 5.0% by mass of chromium, and the chromium is in a mother phase of brass. It can be obtained by extruding an aggregate of brass alloy powder containing a component that dissolves and a component that precipitates at the grain boundary.

  In one embodiment, the 0.2% proof stress value of the brass alloy extruded material is 300 MPa or more. Moreover, the tensile strength is 500 MPa or more.

  In order to improve the machinability of the brass alloy extrudate, in one embodiment, the brass alloy extrudate is added after 0.2 to 2.0% by weight of graphite particles are added to and mixed with the brass alloy powder. The mixed powder aggregate is obtained by extruding. The particle diameter of the graphite particles to be added is preferably in the range of 1 μm to 100 μm.

  The brass alloy member according to the present invention has a brass composition composed of a mixed phase of an α phase and a β phase, contains 0.5 to 5.0% by mass of chromium, and is further nickel, manganese, zirconium, vanadium, titanium. And at least one element selected from the group consisting of silicon, aluminum and tin. Chromium contains a component that dissolves in the mother phase of brass and a component that precipitates at the grain boundaries.

  In order to improve the machinability of the brass alloy member, in one embodiment, the brass alloy member further includes graphite particles.

  A method for producing a brass alloy extruded material according to the present invention has a brass composition comprising a mixed phase of an α phase and a β phase, and rapidly solidifies a brass alloy powder containing 0.5 to 5.0% by mass of chromium. And a step of extruding the aggregate of the rapidly solidified brass alloy powder.

  Preferably, the rapid solidification method is a water atomization method. The heating temperature at the time of extrusion is preferably 650 ° C. or less.

  The manufacturing method in one embodiment includes a step of adding and mixing 0.2 to 2.0% by weight of graphite particles with respect to the brass alloy powder prior to extrusion.

  Including the above description, the effects and the like brought about by the configuration of the present invention will be described in detail in the following items.

It is a SEM (scanning electron microscope) photograph which shows the powder produced by the water atomization method, (a) is 6/4 brass alloy powder without Cr addition, (b) is 6/4 with 0.5 mass% Cr addition. Brass alloy powder, (c) shows 6/4 brass alloy powder with 1.0 mass% Cr added. It is a figure which shows the X-ray-diffraction result of the produced water atomized powder. It is a figure which shows the stress-strain curve of an extruded material. It is a figure which shows the structure | tissue photograph by the optical microscope of an extrusion material, (a) is the extrusion material of the brass alloy compacting billet of 1 mass% Cr addition, (b) is the brass alloy powder compact of 0.5 mass% Cr addition. (C) shows an extruded material of a brass alloy green compact billet without addition of Cr, and (d) shows an extruded material of a brass alloy melted billet without addition of Cr. It is a photograph which shows the SEM image of the extrusion material of the brass alloy compacting billet of 1.0 mass% Cr addition. It is a figure which shows the relationship between the density | concentration of the chromium component which dissolves in the mother phase of a brass, and a proof stress value. It is a figure which shows the relationship between graphite particle addition amount and machinability.

[New brass alloy powder production method]
The inventors of the present invention have studied a method for producing a high-strength, free-cutting brass member that has never been obtained by increasing the strength of the brass itself as a base material. As a method for increasing the strength of brass, generally, a method of adding various additives is employed. For example, high-strength brass is obtained by adding iron, aluminum, manganese, and the like to a copper-zinc alloy, and has high tensile strength of 460 MPa and good corrosion resistance, and is therefore applied to marine propellers and the like. However, this high-strength brass is not guaranteed to have good workability because its elongation is only guaranteed about 15%.

  In order to develop an alloy with a view to adding graphite, it is necessary to produce an unprecedented new brass alloy powder and to extrude this powder aggregate to improve the strength. Conventionally, a melting method has been adopted for the production of brass, but the present inventors have attempted to produce a brass alloy having a new alloy composition by a powder metallurgy method instead of the melting method.

  According to the water atomization method, which is a kind of rapid solidification method, the melt is rapidly solidified by solidification at a very high speed, so that not only a nonequilibrium phase appears in the powder but also fine crystal grains. There is a feature that can be obtained. As a new attempt, the present inventors have added a small amount of chromium (Cr) as a third element to a brass alloy composed of a mixed phase of an α phase and a β phase. A new material was obtained by extruding and solidifying this powder aggregate by hot extrusion.

  Many attempts have been made to improve the properties by adding various additives to brass, but there is no precedent that a transition element is positively added to 6/4 brass by the water atomization method.

  The present inventors propose a new method for adding chromium, which is a refractory metal, to 6/4 brass. As described above, in order to dissolve brass and dissolve chromium therein, the molten metal must be heated to the melting point of chromium, but such heating temperature exceeds the boiling point of zinc. Therefore, in reality, in view of the high vapor pressure of zinc, it may be impossible to raise the temperature of liquid brass to the melting point of chromium.

  As another method for adding chromium to brass, it is conceivable to use a mother alloy containing chromium. However, since the melting point of the copper-chromium master alloy is also high, zinc is evaporated by the method of adding brass to the melted copper alloy, and the predetermined composition cannot be maintained.

  The present inventors have developed a brass alloy manufacturing method using a commercially available Cu-10% Cr master alloy. In the mother alloy, chromium is dispersed as grains having a size of about 10 to 50 μm, and is not dissolved in copper. The mother alloy is first melted at about 1200 ° C. At this temperature, chromium contained in the mother alloy does not dissolve, so it remains floating in the copper liquid phase in the solid phase. In this state, add copper and adjust the concentration of chromium to be thin. Then, when the chromium concentration becomes about 4%, the liquid phase becomes a single phase state exceeding the solid-liquid phase line on the phase diagram. In this way, chromium, which is a refractory metal, could be made into a mixed liquid phase with copper. When a predetermined amount of zinc was added in this state and rapidly solidified by the water atomization method, a powder having a non-equilibrium phase in which chromium was forcibly dissolved in brass could be obtained.

  It is also possible to forcibly dissolve vanadium in brass by the same method as described above. However, in the binary phase diagram of vanadium and copper, since the solid-liquid phase line is at a vanadium concentration of about 0.5%, the amount of added vanadium is very small. Therefore, in reality, the addition of vanadium into brass is not only technically difficult, but it is difficult to increase the effect of the addition.

  According to the method developed by the present inventors, the composition of the alloy can be appropriately controlled without evaporating the added zinc as much as possible. In 6/4 brass, it is known that the ratio between the α phase and the β phase changes due to a subtle difference in the amount of the zinc component. It is also known that the difference in the ratio between the α phase and the β phase affects the mechanical properties of the brass alloy.

  Therefore, it can be seen that the above-described powder production method developed by the present inventors is an advantageous method for adding a refractory metal to brass from the viewpoint of composition control of the brass alloy. In addition to this, if nickel and manganese having a relatively low melting point are added, the utility value thereof increases as a powder capable of further improving the strength. Furthermore, if graphite is added to the brass alloy powder thus obtained and extruded, a lead-free free-cutting brass alloy excellent in strength and free-cutting property can be obtained. As described above, since the application range of the present invention is wide, it can be said that the present inventors have paved the way for the development of various types of leadless brass having various mechanical characteristics.

  The conventional typical method of crystal grain refinement was to repeatedly perform plastic working and heat treatment on a member, but if the powder metallurgy method was used as in the present invention, it was already refined as a starting material. Since a powder having a crystal structure is prepared, a special process for miniaturization is not required. In addition, since the material composition is already determined in the powder state, the composition of the final product can be grasped at this stage. In addition to such superiority in production process, the material according to the present invention has several excellent features described below.

[Effect of adding third element]
Usually, chromium hardly dissolves in brass. However, by adopting a rapid solidification method such as the water atomization method, chromium dissolved in the liquid phase is forcibly solid-solved in the mother phase of brass by a certain amount. Further, as the crystal grows during the solidification process, a part of chromium is condensed at the crystal grain boundary and precipitated as fine crystal grains. Strictly speaking, the components that dissolve in the mother phase of brass include components that dissolve and disperse in the mother phase, and components that disperse as precipitates in the mother phase. The chromium component forcibly dissolved in the matrix and the chromium component precipitated at the grain boundaries exhibit different effects on the applied stress. That is, the chromium component forcibly dissolved in the matrix phase suppresses dislocation movement in the crystal and contributes to an improvement in the proof stress value of the brass alloy member. On the other hand, the chromium component deposited at the crystal grain boundary suppresses the grain boundary sliding, causes extreme work hardening, and greatly contributes to the improvement of the tensile strength.

  The effect of adding manganese is as follows. Unlike chromium, manganese basically dissolves in brass. Therefore, manganese does not produce grain boundary precipitates and does not cause extreme work hardening, but acts to improve both the proof stress value and the tensile strength in a balanced manner. The reason seems to be that manganese dissolved in the matrix phase pins dislocations.

  The effect of adding nickel is as follows. Nickel also dissolves completely in brass, but promotes transformation from β phase to α phase in the process of hot extrusion of brass alloy, and forms a fine α phase in the crystal, greatly contributing to improvement in yield strength. . However, since nickel does not contribute to work hardening, the maximum tensile stress is not much different from a powder extruded material to which nickel is not added.

  Chromium, manganese, and nickel are transition elements that appear in the fourth period of the periodic table, but have different effects when added to brass as described above, and they behave completely differently. The reason is that each transition element strengthens brass by a different mechanism. Therefore, if two or more elements are added, each effect is considered to be manifested.

  Furthermore, from the above research results, it has become possible to infer the behavior when other elements are added. Vanadium, which is a transition element in the fourth period of the periodic table, has an equilibrium diagram very similar to chromium. Therefore, if vanadium is added and the atomized powder is made in the same way as the addition of chromium, vanadium components that are forcibly dissolved in the matrix and vanadium components that precipitate at the grain boundaries appear, and strengthening is the same as chromium. The mechanism can improve the performance of brass.

  In addition to the above elements, titanium, silicon, aluminum, tin, and the like, which are generally known as brass strengthening elements, are expected to work effectively for strengthening chromium-added brass as an auxiliary additive element.

[Rapid solidification method]
Factors in which the effects of the present invention appear remarkably are not only to produce a non-equilibrium phase and fine crystal grains by producing brass alloy powder by a rapid solidification method, but also work hardening using grain boundary precipitation of chromium. It is in having caused. The present inventors used a water atomization method as an example of the rapid solidification method. The feature of the water atomized powder having a 6/4 brass composition is that it becomes a β phase which is a nonequilibrium phase. This will be described more specifically. In the rapid solidification process of the 6/4 brass alloy, the portion beyond the solid-liquid phase line is in the β phase region, so that the powder solidifies as the β phase. If it is slowly cooled as it is, it should transform into a mixed phase of α and β phases, but this phase transformation hardly occurs due to the high degree of rapid cooling. When the temperature of the β-phase powder is raised during the hot working process, a phase transformation from the β-phase to the α-phase occurs, resulting in a mixed phase.

  Certain types of additive elements exhibit the effect of keeping the β phase stable. Chromium and manganese were found to delay the transformation to α phase. This is an effect of suppressing atomic diffusion in the crystal grains, and it is considered that the effect of maintaining the non-equilibrium phase formed by rapid solidification is high.

  In the present invention, the grain hardening precipitates in the solidification process suppress the grain boundary sliding, so that the work hardening phenomenon is remarkably exhibited. Preferably, the size of the grain boundary precipitate is controlled to a size (maximum length) of about 100 nm to 500 nm. In addition, the dispersion state of the precipitate is an important factor, and it is ideal that the precipitate is uniformly dispersed in the structure. Therefore, it is desirable that the raw material powder is homogeneous. If the atomization method is used as the powder preparation method, the solidification rate and the accompanying powder particle size can be easily controlled.

[Extrusion]
The extrusion temperature is a very important factor for improving the strength of the brass alloy extruded material. The lower the extrusion temperature, the better. In order to extrude the powder aggregate, it is necessary to heat the powder. When this heating temperature is high, atomic diffusion is accelerated, and the nonequilibrium phase formed by rapid solidification approaches a thermal equilibrium state. Therefore, it is important to extrude the brass alloy powder aggregate at the lowest temperature at which extrusion processing is possible. A preferable extrusion temperature is 650 ° C. or lower. It is difficult to determine the lower limit of the extrusion temperature. This is because the lower limit temperature is determined by the size of the extrusion billet, the extrusion ratio, the maximum extrusion load of the apparatus, and the like. If extrusion at 500 ° C. is possible, it can be said that the temperature is an appropriate condition, but in reality, it seems that 550 ° C. or higher is necessary for the extrusion process.

  At the time of extrusion, the actual extrusion temperature is determined by the influence of two factors, a temperature drop due to heat radiation of the billet and a temperature rise due to extrusion pressure. Therefore, it is not practical to define the extrusion temperature, and it is practical to control the heating temperature of the billet. In the brass extrusion experiment, when the heating control temperature of the billet is 650 ° C., 48 seconds may be required until the extrusion starts. Compared with the data obtained in the simulation experiment, the extrusion start temperature at this time is 577 ° C.

  The present inventors have found that a material having higher strength can be obtained by controlling the extrusion speed when extruding the chromium-containing brass alloy powder aggregate. As an extrusion condition for obtaining a material having higher strength, extrusion at a low temperature is effective, and further, an improvement in strength is expected by lowering the extrusion speed. This will be described later based on the experimental results.

  In order to improve the machinability of the brass alloy extruded material, graphite particles may be added to and mixed with the chromium-containing brass alloy powder, and this mixed powder aggregate may be extruded. In order to develop the machinability improving effect, it is necessary to add 0.2 to 2.0% by weight of graphite particles to the chromium-containing brass alloy powder. The particle diameter of the added graphite particles is preferably in the range of 1 μm to 100 μm.

[Amount of element added]
There is an appropriate amount of the third element added depending on various elements.

  For chromium, an improvement in yield strength was observed with the addition of 0.5% by mass. Further, when the addition amount of chromium was increased to 1% by mass, no difference was observed in the proof stress value, but the tensile strength was very high. Therefore, the addition amount of chromium is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more.

  The upper limit of the chromium content is 5.0% by mass. Due to limitations in the powder production stage, the upper limit of the chromium concentration in the copper-chromium liquid phase is 4%. When zinc is added here, the chromium content is 2.4% by mass. It is possible to increase the chromium content by increasing the melting temperature of copper-chromium. For example, when the melting temperature is increased to 1300 ° C., chromium can be dissolved to a concentration of 8%, and the chromium content when zinc is added here is 5.0% by mass. However, at this temperature, the vapor pressure of zinc becomes too high, making composition control difficult. Therefore, a more preferable upper limit of the chromium content is 2.4% by mass.

  Vanadium causes grain boundary precipitation even in a very small amount. Considering that the upper limit of the vanadium concentration in the liquid phase state of copper-vanadium is 0.5%, vanadium should be added to near the upper limit in order to maximize the effect of vanadium. In that case, the concentration of vanadium becomes 0.3 mass% by adding zinc. In order to make the vanadium concentration higher than this value, it is necessary to raise the melting temperature. However, at a temperature of 1200 ° C. or higher, the vapor pressure of zinc becomes too high, making it difficult to produce a powder with an optimal composition. Therefore, the effect of vanadium addition must be limited, and strengthening in combination with other elements is necessary.

  There are already many research examples of the effects obtained by adding manganese to brass, and it has been put into practical use as high manganese brass. In the present invention, the brass alloy can be further strengthened by supplementarily adding manganese in combination with the above chromium addition or chromium and vanadium addition. As manganese addition amount, it confirmed that a sufficient effect was acquired with 0.5 mass%. According to the conventional research example, it is recognized that increasing the amount of manganese added significantly reduces the workability of the material. Therefore, the preferable upper limit of the amount of manganese added is 7 mass% or less, which is a range in which no compound is formed. It is. The more preferable amount of manganese added is 1 to 3% by mass. If this amount is exceeded, the elongation is lowered and the workability of brass may be lowered.

  Since nickel is completely dissolved in copper, any amount can be added and alloyed in the Cu—Zn—Ni system. Accordingly, in the present invention, there is no upper limit on the amount of nickel added. The addition of nickel brings about a special effect of raising only the proof stress value, and a proof stress value exceeding 300 MPa can be realized with an addition amount of 1% by mass.

  It goes without saying that the proof stress value is more important than the tensile strength from the practical viewpoint of the alloy member. The greatest effect for the present invention is that a predetermined amount of chromium is contained in 6/4 brass, but more advantages can be obtained by further adding nickel. Since chromium has a high melting point, it is not easy to add even a trace amount. As a technique to overcome this, the use of thermal equilibrium in metallurgy has already been explained. In order to exhibit the effects of chromium and nickel simultaneously, it is natural to add both elements. In this case, there is an easier method as an addition method. That is, in order to add only chromium, the above-described process is performed. However, in order to add nickel at the same time, it is preferable that the mother alloy contains chromium and nickel from the beginning.

  Nickel-chromium alloys are commercially available, and their melting point decreases to 1345 ° C. when alloyed. It is possible to melt this alloy and copper using a high frequency furnace. The mixing ratio of nickel and chromium is 1: 1, but it is much easier to make molten metal than using a copper-chromium master alloy. If nickel is added using this method, the preferable upper limit of the amount of nickel added is 2.4% by mass, similarly to chromium.

  It is possible to increase the amount of nickel added by changing the mixing ratio of the master alloy of nickel and chromium. Increasing the amount of chromium added to the mother alloy raises the melting point rapidly, increasing the difficulty of powder production. However, increasing the nickel ratio does not increase the melting point and does not exceed the melting point of nickel. Therefore, it is possible to make a nickel-rich powder, and it is possible to increase the amount of nickel added. The upper limit value of the addition amount of nickel is not particularly limited, but it is desirable to keep the addition of 5% by mass or less as a range that does not impair the properties as brass. If the nickel content is within this range, it is possible to produce an alloy having desired mechanical properties, and it can be applied to a wide range of applications.

  With respect to other additive elements, the effect of addition is exhibited at about several percent, at least 0.1% or more. Appropriate amounts and combinations of various elements vary depending on the mechanical properties required. From the viewpoint of improving the strength, zirconium exhibits a crystal grain refining effect. Therefore, even when added in 0.1%, the effect is sufficiently recognized, and it can be said that it is a clear strengthening element from Hall Petch's rule of thumb.

  Titanium, aluminum, and the like increase the strength of the matrix phase by solid solution strengthening, so that the effect is exhibited even when added in a trace amount of 1% or less.

  Silicon is an element usually used for dispersion strengthening, and an addition amount of about 3% is an appropriate amount. However, the addition may not necessarily lead to strengthening in consideration of other elements. In particular, in the alloy system of the present invention, if the chromium precipitation site and the silicon dispersion site are at the same location, the strengthening effect cannot be obtained. Accordingly, the amount of silicon added is limited by the amount of chromium added, and it can be said that it is preferable that the total amount of chromium and silicon is 3% or less.

  Tin is solid-solved at about 0.3% and expresses the effect as a strengthening element. However, when the addition amount is increased, the γ phase appears, which causes embrittlement. It can be said that the range of% -0.5% is suitable.

[Preparation of powder]
From a brass material of Cu-40% Zn, brass powder without addition of Cr, brass powder with addition of 0.5 mass% Cr, and brass powder with addition of 1.0 mass% Cr were prepared by a water atomization method. The chemical composition of the powder is shown in Table 1, and an SEM (Scanning Electron Microscope) photograph of the appearance of the powder is shown in FIG. 1A shows 6/4 brass alloy powder to which Cr is not added, FIG. 1B shows 6/4 brass alloy powder to which 0.5 mass% Cr is added, and FIG. 6/4 brass alloy powder added with 0% by mass Cr is shown.

  The X-ray diffraction result of the produced powder is shown in FIG. Only the β phase was detected in the brass alloy powder containing no Cr and the brass alloy powder containing 0.5% by mass of Cr. In the brass alloy powder to which 1.0 mass% Cr was added, two phases of α phase and β phase were detected. In the case of the 6/4 brass composition, when it exceeds the solid-liquid phase line from the liquid phase, it becomes β phase, and the rapidly solidified powder is generally cooled without undergoing α transformation. As a result of examining the brass alloy powder added with 1.0 mass% Cr in detail, it was in a mixed state of α phase powder and β phase powder. It is thought that a powder having undergone α-transformation was generated due to a difference in cooling rate between individual powders during the atomization process. Since Cr exists as fine particles, no clear diffraction peak was detected by X-ray diffraction.

[Extrusion of brass alloy powder containing 1.0 mass% Cr]
A powder of composition 59% Cu-40% Zn-1% Cr produced by the water atomization method was compacted at 600 MPa to obtain an extrusion billet. This billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were four types of 650 ° C., 700 ° C., 750 ° C., and 780 ° C. The billet was processed with an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

  A tensile test piece having a distance of 10 mm between the grades and 3 mm around the waist was cut out from the bar, and a tensile test was performed to measure a 0.2% proof stress value and a maximum tensile strength. The results are shown in Table 2.

  As is clear from the results of Table 2, the billet extruded at a temperature of 650 ° C. showed high values in the maximum tensile strength and the 0.2% proof stress value. As the heating temperature was raised, these mechanical strengths tended to decrease. Accordingly, the heating temperature of the billet before extrusion is preferably 650 ° C. or less.

[Extrusion of brass alloy powder containing 0.5 mass% Cr]
A 59.5% Cu-40% Zn-0.5% Cr powder produced by the water atomization method was compacted at 600 MPa to obtain an extrusion billet. This billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were four types of 650 ° C., 700 ° C., 750 ° C., and 780 ° C. The billet was processed with an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

  A tensile test piece having a distance of 10 mm between the grades and 3 mm around the waist was cut out from the bar, and a tensile test was performed to measure a 0.2% proof stress value and a maximum tensile strength. The results are shown in Table 3.

  As is apparent from the results in Table 3, the billet extruded at a temperature of 650 ° C. showed high values in the maximum tensile strength and the 0.2% proof stress value. As the heating temperature was raised, these mechanical strengths tended to decrease. Accordingly, the heating temperature of the billet before extrusion is preferably 650 ° C. or less.

  As can be seen from the comparison with the results in Table 2, the 0.2% proof stress value was almost the same for the 0.5% Cr addition and the 1.0% Cr addition. Therefore, it was recognized that the proof stress value is maintained even if the amount of chromium to be added is small. However, the maximum tensile strength decreases as the chromium content decreases. This is supported by the fact that the yield strength value is determined by the amount of chromium that is forcibly dissolved, whereas the maximum tensile stress is that the work hardening degree is increased due to precipitation of excess chromium at the grain boundaries.

[Extrusion of brass alloy powder containing 1.0 mass% Ni]
A powder of composition 59% Cu-40% Zn-1.0% Ni produced by the water atomization method was compacted at 600 MPa to obtain an extrusion billet. This billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were four types of 650 ° C., 700 ° C., 750 ° C., and 780 ° C. The billet was processed with an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

  A tensile test piece having a distance of 10 mm between the grades and 3 mm around the waist was cut out from the bar, and a tensile test was performed to measure a 0.2% proof stress value and a maximum tensile strength. As a result, the billet heated at 650 ° C. and extruded had a 0.2% proof stress of 311 MPa and a maximum tensile strength of 479 MPa. As the heating temperature was raised, these mechanical strengths tended to decrease. Accordingly, the heating temperature of the billet before extrusion is preferably 650 ° C. or less.

[Extrusion of 0.7% by mass Mn added brass alloy powder]
A powder of composition 59% Cu-40% Zn-0.7%% Mn produced by the water atomization method was compacted at 600 MPa to obtain an extrusion billet. This billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were four types of 650 ° C., 700 ° C., 750 ° C., and 780 ° C. The billet was processed with an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

  A tensile test piece having a distance of 10 mm between the grades and 3 mm around the waist was cut out from the bar, and a tensile test was performed to measure a 0.2% proof stress value and a maximum tensile strength. As a result, the billet extruded at 650 ° C. had a 0.2% proof stress of 291 MPa and a maximum tensile strength of 503 MPa. As the heating temperature was raised, these mechanical strengths tended to decrease. Accordingly, the heating temperature of the billet before extrusion is preferably 650 ° C. or less.

[Extrusion of Cr-free brass alloy powder]
A powder of composition 60% Cu-40% Zn produced by the water atomization method was compacted at 600 MPa to obtain a billet for extrusion. This billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were four types of 650 ° C., 700 ° C., 750 ° C., and 780 ° C. The billet was processed with an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

  A tensile test piece having a distance of 10 mm between the grades and 3 mm around the waist was cut out from the bar, and a tensile test was performed to measure a 0.2% proof stress value and a maximum tensile strength. The results are shown in Table 4.

  As is apparent from the results in Table 4, the billet extruded at a temperature of 650 ° C. showed high values in the maximum tensile strength and the 0.2% proof stress value. As the heating temperature was raised, these mechanical strengths tended to decrease. Accordingly, the heating temperature of the billet before extrusion is preferably 650 ° C. or less.

[Extrusion of molten billet of brass alloy without addition of Cr]
A melted billet having a composition of 60% Cu-40% Zn was heated in an electric furnace for extrusion. The temperature conditions of the heating electric furnace were four types of 650 ° C, 700 ° C, 750 ° C, and 780 ° C. The billet was processed with an extruder at an extrusion speed of 3 mm / s and an extrusion ratio of 37 to obtain a bar.

  Tensile test pieces with a distance between scores of 10 mm and a waist circumference of 3 mm were cut out from the bar, and a tensile test was performed. As a result, the billet heated at 650 ° C. and extruded had a 0.2% proof stress of 226 MPa and a maximum tensile strength of 442 MPa.

[Comparison of maximum tensile strength and 0.2% proof stress]
The maximum tensile strength and 0.2% proof stress value of the brass alloy extruded materials that were extruded by heating various billets to a temperature of 650 ° C. were compared. Moreover, the stress-strain curve of an extruded material is shown in FIG. The billets to be compared are a melted billet made of brass alloy containing no Cr, a brass alloy green compact billet containing no Cr, a brass alloy green billet containing 0.5% Cr, and a brass alloy containing 1.0% Cr. There are four types of green compact billets.

  From FIG. 3 and Table 5, the following can be understood. First, when comparing two types of brass alloy billets containing no Cr, the green compact billet shows higher values in both the maximum tensile strength and the 0.2% proof stress value than the melt billet. Specifically, by using a green compact billet, the maximum tensile strength is improved by 5.4% and the 0.2% proof stress value is improved by 20.7%. From this point alone, the advantages of powder metallurgy are clear.

  Furthermore, comparing the green compact billet with 1.0% by mass of chromium and the molten billet without addition of Cr, the extruded material of the green compact billet with 1.0% by mass of Cr has its maximum tensile strength. The strength is improved by 27.8% and the 0.2% proof stress value is improved by 40.2%. It is considered that the 0.2% proof stress value is greatly improved due to the solid solution strengthening by the forced solid solution chromium.

  It can also be seen that the maximum tensile strength of the Cr-added green compact billet is greatly improved compared to the Cr-free green compact billet. This is because, in the solidification process of the powder manufacturing process, chromium that could not be completely dissolved is concentrated at the crystal grain boundaries, resulting in segregation of chromium grain boundaries, and spherical precipitates having a diameter of about 100 nm to 500 nm. The main cause is considered to be the grain boundary triple point or the grain boundary. Such fine precipitates acted as a great resistance against grain boundary sliding during plastic deformation, and as a result showed a high degree of work hardening.

[Tissue observation result]
FIG. 4 shows the result of observation of the structure of the extruded material, which was extruded by setting the billet heating temperature to 650 ° C., using an optical microscope. 4A is an extruded material of a brass alloy green compact billet with 1% by mass Cr added, FIG. 4B is an extruded material of a brass alloy green compact billet with 0.5% by mass Cr added, and FIG. 4C is Cr. An extruded material of an additive-free brass alloy green compact billet, (d) shows an extruded material of an brass-added brass alloy melt billet.

  As is apparent from comparative observation of the photograph in FIG. 4, the green compact billet extrudate has finer crystal grains than the melt billet extrudate. In the case of the brass alloy melt billet extruded material, the crystal grain size is 3 to 10 μm, while the crystal grain size of the Cr-free brass alloy green compact billet extruded material is 1 to 6 μm. Moreover, when it becomes a brass alloy green compact billet extrusion material of Cr addition, it is recognized that further refinement | miniaturization is progressing with a crystal grain size of submicron-5 micrometers.

  With grain refinement, the proof stress value increased according to the Hall-Petch empirical rule. In the structure of the Cr additive, black dot-like fine precipitates of 1 μm or less were observed at the grain boundaries. As a result of EDS analysis, these precipitates were identified as Cr.

  FIG. 5 shows an SEM image of an extruded material of a brass alloy green compact billet containing 1 mass% Cr.

  In addition, in the above description, although it described centering on the brass alloy powder or the brass alloy powder extrusion material, this invention is applicable also to a brass alloy member. That is, the brass alloy member has a brass composition composed of a mixed phase of α phase and β phase, contains 0.5 to 5.0% by mass of chromium, and further nickel, manganese, zirconium, vanadium, titanium, silicon, It contains at least one element selected from the group consisting of aluminum and tin.

[Increase in yield stress (YS)]
It is recognized that the addition of chromium increases the yield stress of brass alloy members, but it is the chromium that contributes to the increase in the yield stress, especially chromium that dissolves and disperses in the parent phase of brass. It is an ingredient. The amount of chromium dissolved in the matrix was calculated from the amount of chromium added by quantifying the precipitates using the results of the structural analysis.

  The vertical axis represents the difference between the yield stress of the brass alloy member without addition of chromium and the yield stress of the brass alloy member with addition of chromium, and the horizontal axis represents the concentration (%) of the chromium component dissolved in the matrix. Is FIG. When the chromium solid solution amount was 0.22%, the increase in yield stress was 34 MPa, and when the chromium solid solution amount was 0.35%, the increase in yield stress was 54 MPa. Thus, it was confirmed that the yield stress increased in proportion to the concentration of chromium dissolved in the parent phase of brass.

[Improvement of free machinability by adding graphite particles]
In the production of a brass alloy extruded material by powder extrusion, by adding graphite particles, it can be made lead-free and the adverse effects on the environment can be suppressed. Although graphite has been added to general brass in the past, there is no precedent for adding graphite to a brass alloy whose strength has been improved by adding chromium. Therefore, graphite was added to brass whose strength was improved by adding chromium, and an attempt was made to improve machinability.

  The average particle size of the graphite particles used was 5 μm. The chromium-containing brass powder produced by the water atomization method and the graphite particles were mixed by a mechanical stirring method. This mixed powder was used as a green compact billet in the same manner as described above, and subjected to hot extrusion to obtain a bar. The amount of graphite particles to be added was three types of 0.5 wt%, 0.75 wt%, and 1.0 wt% with respect to the chromium-containing brass alloy powder.

  FIG. 7 is a graph showing the relationship between the graphite particle addition amount and the machinability. It was confirmed that if the graphite particles were added to the chromium-containing brass alloy powder and extruded, the machinability improved dramatically. The machinability was evaluated by measuring the test time of a penetration test using a drill. The test piece was a round bar cut to a length of 5 cm, and a penetration test was performed with a drill diameter of 4.5 mm. A load of 1.3 kgf was applied to the drill, and the spindle rotation speed was set to 900 rpm. Ten tests were performed, and the average time required for penetration was displayed in the graph of FIG.

  In the test piece to which no graphite was added, the drill did not penetrate at all even after cutting for 180 seconds or longer. Since it seemed that the cutting progress of the drill had stopped, it was decided to stop the test for those that did not penetrate in 180 seconds.

  The relationship between the amount of graphite added and the time required for drill penetration was investigated. In the 0.5% chromium-containing brass alloy, what was 180 seconds or more when no graphite was added, but the drill penetrated in an average of 28 seconds with a graphite addition amount of 0.5%. With a graphite addition amount of 0.75% or more, the penetration time was 20 seconds or less, and a dramatic improvement in machinability was recognized. Therefore, in the case of a 0.5% chromium-containing brass alloy, it can be said that addition of 0.75% or more of graphite is a suitable condition for greatly improving the machinability.

  In the 1.0% chromium-containing brass alloy, the penetration time was 180 seconds or more even when 0.5% of graphite was added. When the graphite addition amount was increased to 0.75%, the drill penetrated in an average of 38 seconds. When the graphite addition amount was 1.0%, the penetration time was 20 seconds or less. Therefore, in the case of a 1.0% chromium-containing brass alloy, it can be said that addition of 1.0% or more of graphite is a suitable condition for greatly improving the machinability.

[Improvement of strength by low-speed extrusion]
The present inventors have found that a material having higher strength can be obtained by controlling the extrusion rate of the chromium-containing brass alloy. As extrusion conditions for obtaining a high-strength material, extrusion at low temperature is effective, but the strength can be further improved by lowering the extrusion speed. When the measured value is described, in the case of a brass alloy containing 1.0% chromium, the proof stress value was 317 MPa when the extrusion was performed at a normal extrusion speed (ram speed 3 mm / s), and the maximum tensile strength was 565 MPa. When this extrusion speed was reduced to one tenth (ram speed 0.3 mm / s) and extrusion was performed, the proof stress value was improved to 467 MPa, and the maximum tensile strength was improved to 632 MPa.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

  The present invention can be advantageously used in the manufacture of 6/4 brass alloy members having excellent mechanical properties.

Claims (14)

have a brass composition formed by a mixed phase of α-phase and β-phase, a lead-free brass alloy powder rapidly solidified by a water atomizing method,
Containing 0.5 to 5.0% by mass of chromium,
The chromium is a lead-free brass alloy powder containing a component that dissolves in the mother phase of brass and a component that precipitates at grain boundaries. 2. The lead-free brass alloy according to claim 1, wherein the components that are solid-solved in the mother phase of brass include a component that is dissolved and dispersed in the mother phase and a component that is dispersed as a precipitate in the mother phase. Powder. The lead-free brass alloy powder according to claim 1, wherein the chromium content is 1.0 to 2.4 mass%. The lead-free brass alloy powder according to claim 1, wherein the powder contains at least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum, and tin. A lead-free brass alloy extrudate obtained by extruding an aggregate of brass alloy powder having a brass composition composed of a mixed phase of an α phase and a β phase and rapidly solidified by a water atomization method,
A lead-free brass alloy extruded material containing 0.5 to 5.0% by mass of chromium and containing a component in which the chromium is dissolved in a mother phase of brass and a component that precipitates at a grain boundary. The lead-free brass alloy extruded material according to claim 5, wherein the 0.2% proof stress value is 300 MPa or more. The lead-free brass alloy extruded material according to claim 5 , which has a tensile strength of 500 MPa or more. The lead-free brass according to claim 5, obtained by extruding the mixed powder aggregate after adding and mixing 0.2 to 2.0% by weight of graphite particles with respect to the brass alloy powder. Alloy extruded material. The lead-free brass alloy extruded material according to claim 8, wherein a particle diameter of the added graphite particles is in a range of 1 µm to 100 µm. The lead-free brass alloy extruded material according to claim 5, wherein the size of crystal grains of the brass alloy extruded material is 5 µm or less. The lead-free brass alloy extruded material according to claim 5, wherein a diameter of a chromium precipitate existing at the crystal grain boundary is 100 nm to 500 nm. a step of producing a lead-free brass alloy powder having a brass composition composed of a mixed phase of an α phase and a β phase and containing 0.5 to 5.0 mass% of chromium by a water atomization method ;
And a step of extruding an aggregate of brass alloy powder rapidly solidified by the water atomizing method, a manufacturing method of a lead-free brass alloy extruded material. The manufacturing method of the lead-free brass alloy extrusion material of Claim 12 whose heating temperature at the time of the said extrusion process is 650 degrees C or less. The manufacturing method of the lead-free brass alloy extrusion material of Claim 12 provided with the process of adding 0.2-2.0 weight% graphite particle | grain with respect to the said brass alloy powder prior to the said extrusion process, and mixing. .